America's Chernobyl

Timeline of radiation incidents and exposure events

Compiled by Nicole Yakashiro

A note: Drafting a timeline of the radiation and exposure events at Hanford is a challenging process. It is necessarily incomplete. Due to the nature of radioactive contamination, it is difficult to trace with certainty how and to what degree isotopes have impacted human and non-human biology overtime.

Nuclear contamination has, as historian Kate Brown articulates, “no discrete boundaries” (183). Likewise, much of the radiation offsite (for downwinders) has been “chronic” and undocumented, compared to the incidents more likely to be recorded onsite (Steele, “Hanford’s Bitter Legacy,” 19).

This makes an events-based timeline largely insufficient. Citing sociologist Charles Perrow who wrote on the Three Mile Island accident, Brown emphasizes that “the complexity of high-risk nuclear industries ‘outruns all controls’” (180).

Compared to other sites, like the Nevada Test Site, where releases were mostly visible to the public in the form of mushroom clouds, Hanford’s releases were, as lawyer and downwinder activist Trisha Pritikin writes, both “invisible and inaccessible to the public,” even though the site has released more radiation than any other US nuclear production facility.


  • 1942-1943: Hanford is selected as a plutonium production facility for the Manhattan Project. Approximately 1,500 residents, both settlers and Indigenous people, are forced out of the region with little notice. Construction begins on the Hanford Engineer Works by the DuPont corporation. They “aggressively” recruit workers from the South, a substantial number of whom are African Americans. Most are unaware of the risks involved, as what the plant is making is top secret. For more on the experience of Black workers at Hanford, see: Robert Bauman, “Jim Crow in the Tri-Cities, 1943-1950,” The Pacific Northwest Quarterly 96, no. 3 (2005): 124.


  • 1944: In 1944, Hanford begins to release unfiltered airborne iodine-131 (approximately 537,000 curies) as well as other nuclear waste into the ground. Though high level releases have been attributed to the needs of war time, they continued until 1956 According to the Hanford Environmental Dose Reconstruction Study, some 270,000 people in Hanford area received low doses of radiation (i.e. 1.7 rad), but as many as 13,500 people received doses 1,300 times above what is considered safe from contaminated milk (i.e. 33 rad). Babies and small children were said to have received anywhere from 650 to 2900 rad. People downstream of Hanford received 1.7 rad doses of radioactive phosphorus from water and fish from the Columbia River. For more on measuring radioactive material, click here.


  • 1945: Plutonium produced at Hanford is used in the atomic bombs detonated in July at Alamogordo, New Mexico for the Trinity Test and in the bomb dropped on Nagasaki, Japan on 9 August 1945. (The bomb dropped on Hiroshima used uranium from Oak Ridge, Tennessee.) 


  • 1946: The Manhattan Project ends with the passing of the Atomic Energy Act and General Electric becomes the primary contractor at Hanford, from 1946-1964. 


  • 1947: Starting in 1947, Hanford conducts monthly airborne releases of iodine-131, averaging 100-2000 curies. This coincides with Hanford’s first postwar expansion (1947-1949) estimated to cost $350 million. 


  • 1948: Filters are finally used on stacks at Hanford to offset airborne releases. And yet, pounds of nuclear waste are released into the Columbia River.


  • 1949: Hanford conducts the Green Run experiment, intentionally dispersing “raw” (or green) radioactive material (7,780 curies of iodine-131 and 20,000 curies of xenon-133) into eastern Washington, from Spokane, WA to Dalles, OR. The site processed one ton of irradiated uranium cooled only 16 days (the normal cooling period is 83 to 101 days) and released the waste in a 200 by 40-mile plume. The public was not informed. Journalist Karen Dorn Steele has compared this to the famous Three Mile Island accident in 1979 where 15-24 curies of iodine were released leading to an evacuation of local residents and other public health precautions. The joint AEC-US Air Force experiment was classified for 36 years. 


Image: Steele, “Hanford’s Bitter Legacy,” 20.
  • 1950s: Hanford reactors release up to 1,600 curies of nuclear waste per day into the Columbia River through its cooling water.  


  • 1951: Reactors fail to remove iodine during reprocessing and release approximately 34,360 curies of nuclear waste. 


  • 1952: A worker at Hanford, Ernest Johnson, dies suddenly, coinciding with a “Class I” radiation incident at the plant. Though his death is ruled unrelated, his family and others are suspicious. As historian Kate Brown notes, these types of undisclosed incidents at Hanford are common. 


From 1952 to 1954, Hanford’s REDOX (reduction oxidation) plant releases massive amounts of ruthenium 106-contaminated ammonium nitrate flakes in at least nine separate incidents. During these exposures, managers restrict access to the site because the radiation levels are so high. The flakes reach into Richland (where most workers lived), onto farmers’ fields in the region, and across the Columbia River. Some were so radioactive they burned skin like a “lighted match.” Herbert Parker, Hanford health physicist, discussed the possibility of testing local cattle for contamination, but resisted as he “could not do it without risk of exciting too much comment [from the public].”


  • 1954: The Atomic Energy Act exempts Hanford and other government weapons sites “from the public scrutiny and environmental regulations to which commercial nuclear plants are subject.”


  • 1955: In December, the Hanford F reactor leaks 1.7 million gallons of nuclear waste a day into the Columbia River. That same month, a storm causes extensive damage to the facilities. Both issues take several months to resolve with serious health impacts for workers who often wore no protective clothing. The REDOX plant releases an additional 300 curies of ruthenium-106. 


  • 1956: Between 1956 to 1965, as many as five different radioactive substances are released into the Columbia River. Though experts initially estimated that Hanford’s contaminated groundwater would take 175-180 years to reach the Columbia River, in 1956, nuclear contamination had already been detected outside the site’s boundary.


  • Late 1950s: The media raises concern over the dangers of “radioactive food.” Hanford’s impact on oysters in the Columbia and other foodways in the region garners some attention. 


  • 1961: Across the Columbia River from Hanford, “hundreds of grossly deformed, stunted lambs were born, some stillborn and some surviving only a few days after birth.”


  • 1962: In April, Hanford releases 440 curies of iodine-131 in an unintentional spill. That same month, nearly 1,200 curies of radioactive gasses are released from a plutonium finishing plant.Later in September, Hanford intentionally releases 8 curies of iodine-131. Also in 1962, the first “criticality accident” (an uncontrolled nuclear fission chain reaction) occurs at Hanford, sterilizing one of their employees. 


  • Early 1960s: Hanford Labs receives government funding for medical research, much of it focusing on human experimentation. The labs study the impacts of radioactive materials such as contaminated milk and fish in the Columbia River by having employees and volunteers ingest them. This experimentation builds off of more than a decade of biological testing at Hanford on animals, including salmon, sheep, pigs, pygmy goats, and stray dogs.


Image: HDDR #N1D0007510 Declassified Photos from Safe as Mother’s Milk: The Hanford Project


  • 1965: Hanford Labs is renamed Battelle’s Pacific Northwest Labs and begins its largest human experiment on Walla Walla State prisoners who are paid for offering their bodies as subjects. Much of these studies centre questions of sterility and includes a testes irradiation study. The prisoner research ends in 1971. 


  • 1973: A 115,000-gallon leak in a Hanford tank is publicly announced. The Seattle Post Intelligencer reports that, for 30 years, “billions of gallons of low-level wastes” have been released into the ground around Hanford.


  • 1984: Karen Dorn Steele, a reporter for the Spokane Spokesman Review, hears from a Hanford employee concerned about safety at the site. These claims coincide with those of whistleblower, Casey Ruud, a safety inspector at Hanford who began at the site in 1985. Steele and others, including the Hanford Education Action League, advocate for access to information about Hanford emissions and contamination. 


  • 1985: The Spokesman Review publishes its first article on Hanford downwinders in July. The Washington State Nuclear Waste Board calls for an independent study on downwinders.


  • 1986: Answering to the pressure from the public, namely HEAL, the Environmental Policy Institute, the Physicians for Social Responsibility (PSR), Native American governments, and downwinders themselves, manager of the Richland Department of Enegery Michael Lawrence declassifies 19,000 pages of documents about Hanford. The same year, the Chernobyl nuclear accident occurs, prompting concern among DOE officials and the public. An additional 10,000 pages are released in 1987 which reveal that aquifers and farmers’ wells had been contaminated along the Columbia River. These events initiate government health studies, namely the Hanford Environmental Dose Reconstruction (HEDR) in 1986 and Hanford Thyroid Disease Study (HDTS) in 1988.


  • 1987: The N reactor at Hanford is shut down, but in the process strontium-90 is released into the Columbia River. 


  • 1988-89: The DOE shuts down plutonium production and admits they are faced with a “serious environmental catastrophe in need of cleanup.” There is approximately “seventeen hundred pounds of plutonium-239 scattered among fifty-three million gallons of other poisons and fission products” at the Hanford site. Buried train cars are found containing radioactive animal carcasses, baby diapers, and contaminated soil. In May of 1989, the Tri-Party clean-up Agreement is signed by the Washington State Department of Ecology, the US Environmental Protection Agency, and the US Department of Energy. Clean-up is estimated at $100 billion over 50 years. 


  • 1990: DOE officials admit knowledge of an explosion threat since 1979. The preliminary results of the government’s health studies are announced.


  • 1991: The In re Hanford Nuclear Reservation Litigation legal case begins, in which downwinders must prove that their stated health effects would not have occurred without Hanford’s plutonium production. The case would continue for 25 years. Approximately 5000 plaintiffs file cases, yet only six “bellwethers” are allowed to testify. The nuclear contractors (General Electric, E.I. DuPont de Nemours, Atlantic Richfield Co., United Nuclear and Rockwell International Corp.) had their legal funds paid for by US taxpayers. (For more, see Trisha T. Pritikin’s The Hanford Plaintiffs: Voices from the Fight for Atomic Justice, 2020).


  • 1994: The government’s Hanford Environmental Dose Reconstruction study is published.


  • November, 1994: Karen Dorn Steele publishes a series looking into spending at the Hanford cleanup, called "River of Money"


  • 1996: Fluor Daniel and five other companies replace Westinghouse as contractors. 


  • 1997: In May, a radioactive explosion blows off the lid of a 400-gallon tank (one of thousands) at Hanford.  


  • 1999: Steele writes an article about the dangerous amounts of radioactive strontium-90 found at juvenile salmon and spawning grounds in the Columbia River. 


  • 2002: The final report of the Hanford Thyroid Disease Study is published.


  • 2004: The Northwest Radiation Health Alliance publishes its community-based epidemiology study. 


  • 2015: The confidential final settlements of In re Hanford case are made.


  • 2017: A tunnel used to store radioactive waste at Hanford from 1965 collapses. Though no radioactive waste is determined to be released, Hanford workers and surrounding communities are ordered to take cover.


  • 2019: Ongoing clean-up projects raise concerns about airborne plutonium escaping demolition work area.


  • February, 2019: The cost of the Hanford clean up jumps by $82 billion, bringing the current total up to $242 billion


  • June, 2019: Former Hanford workers win easier access to workers comp for illnessess such as cancer. The Trump administration had challenged the Washington State law for appeal.


  • February 2020: The Trump administration calls to cut funding for Superfund cleanup sites, like Hanford. Previously, the administration called for cost-cutting at sites like Hanford by reclassifying some forms of radioactive waste from "high-risk" to "low-risk" -- meaning that instead of being buried deep underground and following certain protocol, the reclassified waste could be disposed of in "shallow pits."


  • April 2020: Washington's General Accounting Office audits the Hanford cleanup site, finding that contractors have not been keeping up with inspections at aging facilities that could collapse.


Bulletin of the Atomic Scientists. “A Predictable Nuclear Accident at Hanford,” May 17, 2017.


Bauman, Robert. “Jim Crow in the Tri-Cities, 1943-1950.” The Pacific Northwest Quarterly 96, no. 3 (2005): 124–31.


Brown, Kate. Plutopia: Nuclear Families, Atomic Cities, and the Great Soviet and American Plutonium Disasters. Oxford University Press, 2013.


Cary, Annette, and Tri-City Herald. “Workers Uncover Carcasses of Hanford Test Animals.” Seattlepi.Com, January 15, 2007.


“Center for the Study of the Pacific Northwest.” Accessed August 7, 2020.


D’Antonio, Michael. Atomic Harvest: Hanford and the Lethal Toll of America’s Nuclear Arsenal. Crown Pub, 1993.


Dorn Steele, Karen. “Hanford: America’s Nuclear Graveyard.” Bulletin of the Atomic Scientists 45, no. 8 (October 1989): 15–23.


———. “Hanford’s Bitter Legacy.” Bulletin of the Atomic Scientists 44, no. 1 (January 1988): 17–23.


Dorn Steele, Karen, and Jim Lynch. “River of Money at the Hanford Nuclear Reservation | The Spokesman-Review.” The Spokesman-Review.
November 13, 1994.


Findlay, John M., and Bruce W. Hevly. Atomic Frontier Days: Hanford and the American West. University of Washington Press, 2011.


Foster, Heath. “Hanford Blast Not Unique, Probe Finds.” Seattle PI, June 7, 1997.


Gephart, Roy E. “A Short History of Hanford.” Technical Report. Department of Energy, November 1, 2002.


“Hanford Nuclear Site Accident Puts Focus on Aging U.S. Facilities.” Reuters, May 12, 2017.


Jewell, Mark. “State Levies $110,000 Fine in Hanford Blast Department of Energy, Two Contractors Penalized Following 4-Month Investigation.” Spokesman Review, September 19, 1997.


NUSSBAUM, RUDI H., PATRICIA P. HOOVER, CHARLES M. GROSSMAN, and FRED D. NUSSBAUM. “Community-Based Participatory Health Survey of Hanford, WA, Downwinders: A Model for Citizen Empowerment.” Society & Natural Resources 17, no. 6 (July 1, 2004): 547–59.


Pritikin, Trisha T. The Hanford Plaintiffs: Voices from the Fight for Atomic Justice. University Press of Kansas, 2020.


“Safe As Mother’s Milk: The Hanford Project | Background: Experiments.” Accessed August 7, 2020.
The Hanford Project. “Safe As Mother’s Milk: The Hanford Project | Timeline.” The Hanford Project. Accessed August 4, 2020.